Oxidase-promoted gelling of phenolic polymers

ABSTRACT

A method for causing gelling or increase of viscosity of an aqueous medium containing a gellable polymeric material having substituents with phenolic hydroxy groups comprises adding an oxidase, particularly a laccase, to the aqueous medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national application ofPCT/DK95/00317 filed Jul. 26, 1995, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a method for causing gelling orincrease of viscosity of aqueous media containing gellable polymericmaterials having substituents with phenolic hydroxy groups.

BACKGROUND OF THE INVENTION

Certain pectins, e.g. pectin from sugar beets and pectin from spinach,as well as hemicellulosic material from certain cereals, e.g. from wheatand maize, are substituted to some extent with substituents derived fromcertain carboxylic acids (normally substituted cinnamic acids)containing phenolic hydroxy groups. Substances of this type are, forconvenience and brevity, often referred to in the following simply as“phenolic polysaccharides”.

A number of naturally occurring phenolic polysaccharides of theabove-mentioned type are readily available relatively cheaply and are ofproven physiological safety with regard to ingestion by, and contactwith, humans and animals. Such phenolic polysaccharides have numerousapplications relating to their ability to undergo gelling or viscosityincrease under certain conditions. Areas of application of the resultinggelled or viscous products include, but are by no means limited to, thefollowing:

Foodstuff applications: as a thickening and/or stabilising agent insauces, gravy, desserts, toppings, ice cream and the like; as a settingagent in marmelades, jams, gellies and the like; as aviscosity-regulating agent in flavouring extracts and the like.

Medical/medicinal applications: as a material for drug encapsulation; asa slow release vehicle for drug delivery (e.g. oral, anal or vaginal);as a material for a wound or burn dressing.

Agricultural/horticultural applications: as a slow release vehicle forpesticide delivery (i.e. as a biocontainer); as a plant culture medium.

Oxidative cross-linking of phenolic polysaccharides of plant origin(with resultant gelling) is described in, e.g., FR 2 545 101 and WO93/10158, and by J. -F. Thibault et al. in The Chemistry and Technologyof Pectin, Academic Press 1991, Chapter 7, pp. 119-133.

The cross-linking of phenolic polysaccharides may be achieved by purelychemical modification using a powerful oxidant such as, e.g, persulfate[as described in J. -F. Thibault et al. (vide supra) in connection withthe gelling of beet pectins].

With respect to enzyme-catalyzed processes, J. -F. Thibault et al. (videsupra) also describe the gelling of beet pectins using a combination ofa peroxidase and hydrogen peroxide. Similarly, WO 93/10158 describesgelling of aqueous hemicellulosic material containing phenolicsubstituents (e.g. substituents derived from “ferulic acid” (i.e.4-hydroxy-3-methoxycinnamic acid; it does not appear to have beenestablished clearly whether “ferulic acid” embraces cis or transisomeric forms, or both) using an oxidizing system comprising a peroxide(such as hydrogen peroxide) and an “oxygenase” (preferably aperoxidase).

FR 2 545 101 A1 describes a process for modification (including gelling)of beet pectin involving the use of “an oxidizing system comprising atleast an oxidizing agent and an enzyme for which the oxidizing agent inquestion is a substrate”. However, the only types of oxidizing agent andenzyme which are specified and/or for which working examples are givenare hydrogen peroxide and peroxidases, respectively.

The documents outlined briefly above describe, inter alia, the use ofthe resulting modified/gelled materials for medical/medicinal purposes,in cosmetics and/or in foodstuffs. However, neither peroxide treatmentnor chemical modification of substances intended for ingestion (e.g.substances for use in foodstuffs) or for uses which may result in moreor less prolonged contact with, or close proximity to, skin or mucousmembranes are desirable, and such treatments are in fact not permittedin many countries. As will be apparent from the above discussion, thereseems to be a lack of real awareness of the possibility of avoiding suchundesirable treatments, and it is an object of the present invention toprovide an alternative to the existing methods.

SUMMARY OF THE INVENTION

It has now surprisingly been found that gelling or increase in viscosityof aqueous, gellable polymeric materials having substituents withphenolic hydroxy groups, notably phenolic polysaccharides, may beachieved very satisfactorily via the simple addition of an appropriateamount of an enzyme of the oxidase type (vide infra), especially alaccase. Laccases utilize oxygen—very suitably oxygen from theatmosphere—as oxidizing agent, and the use of undesirable reagents suchas peroxides may thus be eliminated with the process of the presentinvention.

Laccases are less powerful oxidation-promotors than, e.g., peroxidases,and it is thus surprising that gelling and/or viscosity increaseaccording to the invention can be achieved in the absence of apowerfully oxidizing peroxide reagent. As mentioned above,laccase-catalyzed oxidation involves oxygen, and the consumption ofoxygen in the process of the invention leads to the possibility ofexploiting the process in a manner which can be advantageous from thepoint of view of increasing the shelf-life of, e.g., foodstuffs ormedicinal products in the preparation of which the process of theinvention is employed, since the consumption of oxygen initially presentin a sealed foodstuffs package or the like will reduce the possibilityof oxidative degradation of the packaged contents.

DETAILED DESCRIPTION OF THE INVENTION

The present invention thus relates to a method for causing gelling orincrease of viscosity of an aqueous medium containing a gellablepolymeric material having substituents with phenolic hydroxy groups, themethod comprising adding an oxidase, preferably a laccase, to theaqueous medium. As already indicated above, preferred gellable polymericmaterials in this connection are phenolic polysaccharides.

Gel Formation

It is believed that the gel formation in aqueous medium occurs as aresult of polymerization via cross-linking between the phenolic groupsof a polymeric material of the type in question (in the following oftenreferred to simply as a “phenolic polymer”), presumably via theformation of stable phenoxy radicals from the hydroxylated aromaticsubstituents. Increasing cross-linking in this manner eventually(normally after a period of time varying from a few minutes up to about24 hours at room temperature) leads to an extended, three-dimensionallycross-linked structure, with attendant gelling.

A given phenolic polymer material of the type in question may, ifdesired, be copolymerized with other monomeric substances (e.g. simplephenols) or polymeric substances (e.g. simple polyphenols, or otherpolymeric materials having appropriate phenolic substituents, includingcertain proteins).

It is well known that the physical properties of gels differ greatlyfrom those of corresponding non-gelled solutions. The physicalproperties of gelled products, and the properties conferred on a productby inclusion of a gel therein, may be characterized by a variety oftechniques.

In one such technique, which is known as “Texture Analysis” and which isemployed in the working examples herein (vide infra), the “strength” orhardness of a gel is measured by compressing the gel to a chosen extent(such as 20%) and at a chosen rate and recording the applied force as afunction of, e.g., time. The gel strength [which is normally given inNewtons per square meter (N/m²)] is then determined as the peak force onthe force-time curve.

Phenolic Polymers

As already briefly indicated above, very suitable types of phenolicpolymers for use in the method of the invention are phenolicpolysaccharides as defined herein. Phenolic polysaccharides areparticularly well suited when the product formed according to the methodis to be employed, for example, in the manufacture of a foodstuff forhuman and/or animal ingestion, as or in the manufacture of a medicinal,therapeutic or other product for ingestion by, or external applicationto, humans or animals.

Other very interesting classes of phenolic polymers in the context ofthe process of, and fields of applicability of, the present inventioninclude peptides (polypeptides) and proteins having phenolicsubstituents. Naturally occurring and synthetic (poly)peptides andproteins having phenolic substituents include those with one or moretyrosine residues in the amino acid sequence.

As also indicated above, a number of readily availablepolysaccharide-based polymers of natural origin (predominantly plantorigin) contain substituents derived from cinnamic or benzoic acid, andthese substances have proved well suited as starting materials inconnection with the formation of gels by the method of the invention.Moreover, as a consequence of their ready biological renewability anddegradability such naturally occurring phenolic polymers are highlyenvironmentally friendly.

Some particularly interesting classes of such substances include thefollowing:

Arabinoxylans:

Arabinoxylans containing phenolic substituents derived from cinnamicacid [e.g. derived from ferulic acid (vide supra)] are obtainable fromcereals, and they represent one class of useful phenolicpolysaccharides. Arabinoxylans contain a backbone of β-1,4-linked xyloseunits with arabinose (α-linked arabinofuranose) side-branches. Thephenolic substituents present in the cereal-derived materials areattached by ester linkages to arabinose groups, e.g. as ferulyl (oftendenoted feruloyl) groups, i.e. 4-hydroxy-3-methoxy-cinnamyl groups. Thearabinoxylans found in the endosperm of cereals have an arabinose:xyloseratio of about 0.6:1 and are susceptible to xylanase degradation.

Heteroxylans:

Certain types of bran (e.g. wheat bran and maize bran) contain phenolicheteroxylans which are far more branched than arabinoxylans and whichmay—in addition to arabinose—contain galactose and glucuronic acid unitsin the side-branches [see, e.g., J. -M. Brillourt and J. -P. Joseleau inCarbohydr. Res. 159 (1987) 109-126, and J. -M. Brillourt et al. in J.Agricultur. Food Chem. 30 (1982) 21-27]. These heteroxylans arepartially resistant to xylanase degradation, and a xylanase-containingenzyme preparation may therefore be used in the purification of theseheteroxylans. Heteroxylans having phenolic substituents based oncinnamic acid ester groups can be isolated from the bran using mildalkaline extraction, since the ester linkages via which the substituentsare attached are relatively alkali-stable.

Pectins:

Pectins obtainable from members of the plant family Chenopodiaceae(which includes beets, spinach and mangelwurzels) contain phenolicsubstituents derived from cinnamic acid. Pectins are made up of “smooth”regions, based on linear homogalacturonan, and “hairy” (ramified)regions, based on a rhamnogalacturonan backbone with side-branches ofvarying length.

The linear homogalacturonan part of pectins is based on chains of1,4-linked α-D-galacturonic acid, and this polygalacturonic acid ismethoxylated to varying degrees—depending on the plant species inquestion—and may (as in e.g. sugar beet pectin) further be partiallyacetylated. Rhamnogalacturonans are polysaccharides with more or lessregularly alternating rhamnose and galacturonic acid residues in thebackbone. The rhamnogalacturonan backbone in the hairy regions ofpectins have acetyl groups on the galacturonic acid residues (cf. H. A.Schols in Carbohydr. Res. 206 (1990) 117-129); the side-branches includeoligo- and polysaccharides such as arabinan and arabinogalactan, whichare linked to the rhamnose in the rhamnogalacturonan backbone.

Sugar beet pectin is especially rich in arabinan. Arabinan containsβ-1,5-linked arabinose in the backbone with α-(1->3)-or α-(1->2)-linkedarabinose residues, whereas arabinogalactan contains β-1,4-linkedgalactose in the backbone, with α-(1->3) or α-(1->2) linked arabinoseresidues. Ferulyl substituents are linked to the arabinose and/or thegalactose in the arabinan and arabinogalactan side-branches of therhamnogalacturonan part. The “ferulic acid” (ferulyl) content in sugarbeet pectin depends upon the method of extraction, but is often about0.6% [cf. F. Guillon and J. -F. Thibault, Carbohydrate Polymers 12(1990) 353-374].

It is known that beet pectin obtained by a process which results inpartial removal of the arabinose residues which are present in beetpectin in the form in which it occurs in, e.g., beet pulp may exhibitimproved gelling properties. Thus, e.g., procedures involving a mildacid treatment and/or a treatment with an α-arabinofuranosidase willimprove the gelling properties of the pectin [F. Guillon and J. -F.Thibault (vide supra)]. For the purposes of the present invention, “mildacid treatment” involves treating the pectin with 0.1M trifluoroaceticacid at 25° C. for 8 hours, 24 hours and 72 hours, or with 0.05Mtrifluoroacetic acid at 100° C. in a sealed tube for 1 to 12 hours.

Pectic materials (i.e. pectins or modified pectins) of theabove-mentioned types—notably sugar beet pectins—are among the preferredtypes of phenolic polymers in the context of the invention.

The phenolic-substituted cinnamic acid ester linkages can be hydrolysedby ferulic acid esterases. Enzymes used in the purification ofpolysaccharides containing substituents of the cinnamic acid type shouldtherefore be essentially free from ferulic acid esterase activity withspecificity towards ferulic acid esters of the polysaccharide inquestion. Under conditions of low water activity, ferulic acid esterasewill catalyse the formation of new ester linkages to carbohydrates, andcan therefore be used to increase the content of ester residues of thephenolic cinnamic acid ester type (e.g. ferulyl residues) in cerealarabinoxylan and pectin from beet (or other members of theChenopodiaceae) and thereby their gelling properties.

Polysaccharides (and other types of polymers) which do not containphenolic residues useful for achieving gelation can be derivatized inorder to render them gellable. Under conditions of low water activity,ferulic acid esterases can be used to attach groups of the cinnamic acidester type (e.g. ferulic acid ester groups) to polymers such as pectin,arabinan, galactan, cellulose derivatives (e.g. hydroxyethylcellulose orcarboxymethylcellulose), galactomannans (e.g. guar gum,hydroxypropyl-guar gum or locust bean gum), beta-glucans, xyloglucans,starch, derivatized starch, bacterial gums (e.g. xanthan), algal gums(e.g. alginate or carrageenan), other polysaccharides or other polymerswith hydroxyl groups.

Ester linkages to phenolic cinnamic acids (or other phenolic carboxylicacids) may also be synthesized by non-enzymatic methods known in theart. Polymers which contain acid groups, such as pectin andcarboxymethylcellulose, can be esterified with polyhydric phenolicsubstances, e.g. ferulic alcohol, sinapyl alcohol or lignin derivatives,in order to obtain a phenolic polymer with the ability to undergooxidative gelation.

As already indicated to some extent, particularly interesting phenolicsubstituents in the context of the present invention include thosecomprising one or two methoxy groups in an ortho-position in thearomatic ring relative to the phenolic hydroxy group [as in the case of,e.g., ferulyl (4-hydroxy-3-methoxy-cinnamyl) substituents].

The concentration of phenolic polymer (e.g. phenolic polysaccharide)present in the aqueous medium employed in the process of the inventionwill normally be in the range of 0.1-10% by weight of the medium, forexample in the range of 0.5-5% by weight. Concentrations of phenolicpolymer in the range of about 1-5% by weight will often be appropriate.

Enzymes

As already indicated, the preferred enzymes in the context of thepresent invention are laccases (EC 1.10.3.2), which are oxidases (i.e.enzymes employing molecular oxygen as acceptor) capable of catalyzingoxidation of phenolic groups. Examples of other potentially useful,phenol-oxidizing oxidases in the context of the invention include thecatechol oxidases (EC 1.10.3.1). The use of mixtures of differentphenol-oxidizing oxidases may also be appropriate in some cases.

Contact of a reaction mixture (containing phenolic polymer and enzyme)with atmospheric air will normally suffice to ensure an adequate supplyof oxygen for the oxidation reaction, although forcible aeration ofreaction mixtures with air, or possibly even substantially pure oxygen,may be advantageous under certain conditions.

Laccases are obtainable from a variety of microbial sources, notablybacteria and fungi (including filamentous fungi and yeasts), andsuitable examples of laccases include those obtainable from strains ofAspergillus, Neurospora (e.g. N. crassa), Podospora, Botrytis, Collybia,Fomes, Lentinus, Pleurotus, Trametes [some species/strains of which areknown by various names and/or have previously been classified withinother genera; e.g. Trametes villosa=T. pinsitus=Polyporus pinsitis (alsoknown as P. pinsitus or P. villosus)=Coriolus pinsitus], Polyporus,Rhizoctonia (e.g. R. solani), Coprinus (e.g. C. plicatilis), Psatyrella,Myceliophthora (e.g. M. thermophila), Schytalidium, Phlebia (e.g. P.radita; see WO 92/01046), or Coriolus (e.g. C. hirsutus; see JP2-238885).

A preferred laccase in the context of the invention is that obtainablefrom Trametes villosa.

Before adding the enzyme (e.g. a laccase) to a solution containingphenolic starting material(s) (e.g. a phenolic polysaccharide), it willgenerally be preferable to adjust the pH of the solution to a valueequal to, or in the vicinity of, the optimum pH for the enzyme inquestion.

For laccases, the amount of laccase employed should generally be in therange of 0.01-1000 kLACU per kg of polysaccharide, preferably 0.05-100kLACU/kg of polysaccharide, and will typically be in the range of0.1-100 kLACU per kg of polysaccharide (LACU is the unit of laccaseactivity as defined below; 1 kLACU=1000 LACU).

Determination of Laccase Activity (LACU)

Laccase activity as defined herein is determined on the basis ofspectrophotometric measurements of the oxidation of syringaldazin underaerobic conditions. The intensity of the violet colour produced in theoxidation reaction is measured at 530 nm.

The analytical conditions are: 19 μM syringaldazin, 23.2 mM acetatebuffer, pH 5.5, 30° C., reaction time 1 minute.

1 laccase unit (LACU) is the amount of enzyme that catalyses theconversion of 1 μM of syringaldazin per minute under these conditions.

Applications

As already indicated above, gelled products or products of increasedviscosity produced according to the invention have a wide range ofapplications, e.g. in the food and feed areas, the pharmaceutical andagricultural areas, and the personal care/personal hygiene area.

A particularly interesting and valuable property of certain gel products(“hydrogels”) produced according to the invention is their ability whendried or dehydrated to absorb many times their own weight of liquid(more particularly water or an aqueous medium, e.g. a body fluid such asurine or blood) Materials exhibiting such absorption properties aresometimes referred to as “superabsorbent” materials.

Initially, the most important property in connection with superabsorbentmaterials was regarded as being the total absorption capacity.Subsequently, however, a number of other properties have been recognizedas being of great importance. These properties include the following:rate of absorption; ability to resist so-called gel blocking (wherebypart of the absorbing material becomes saturated with liquid andprevents access of further liquid to the remaining part of the absorbingmaterial); and absorption under load (AUL; i.e. the ability of asuperabsorbent material to absorb liquid when subjected, e.g., tocompression or to centrifugal forces.

Certain products obtainable according to the present invention, e.g.gelled products produced from pectic materials such as sugar beetpectin, have been found to very well suited for use as absorbentmaterials of the above-outlined type, and the present inventionencompasses such use. As examples of applications of theliquid-absorption properties of dried or dehydrated gel productsobtainable according to the invention may be mentioned their use as anabsorbent in disposable nappies or diapers for infants or for personssuffering from incontinence, or in disposable feminine hygiene products(sanitary towels, sanitary napkins, panty protectors, tampons and thelike).

Drying or dehydration of gelled products obtainable according to theinvention may suitably be achieved, for example, by drying them undervacuum at ambient temperature or at a moderately elevated temperature(e.g. a temperature up to about 40° C.). In some cases a pre-treatmentsuch as washing with a water-miscible organic solvent (e.g. acetone,ethanol or the like) may be of value in reducing the water content of agel prior to final drying by, for example, vacuum treatment.

The present invention is further illustrated by the following examples,which are not in any way intended to limit the scope of the invention asclaimed.

EXAMPLE 1

Gelation of Feruloyl-Arabinoxylan

A gel of Corn Bran Extract (feruloyl-arabinoxylan powder) was producedin the following way:

Demineralised water (198 ml) was heated to 90° C., and Corn Bran Extract(2.00 g; obtainable from GB Gels Ltd, Wales, UK) was added undervigorous stirring. 5 ml aliquots of the resulting solution were thenpoured (temperature 40° C.) into 10 ml aluminium forms. Laccase[Trametes villosa laccase; produced by Novo Nordisk A/S, Bagsvaerd,Denmark] was added at three different concentration levels: 0.18 LACU/gCorn Bran Extract, 1.8 LACU/g Corn Bran Extract and 18 LACU/g Corn BranExtract. A control was also prepared, containing 18.0 LACU ofinactivated laccase (inactivated by heating at 85° C. for 15 min) per gof Corn Bran Extract. The aluminium sample forms were covered with a lidand left to stand at room temperature.

The hardness of the various gelled samples was measured the followingday by Texture Analysis (vide supra), using an SMS Texture AnalyzerTA-XT2 (Stable Micro Systems; XT.RA Dimensions, Operating Manual version37) with a flat compression cylinder of diameter 20 mm.

The measurement conditions were as follows:

% gel deformation (compression): 20%

Rate of deformation (compression): 2 mm/sec

pH of all samples remained unadjusted at 4.9.

The results obtained are given below (average of four measurements). Itshould be noted that for simplicity, the peak force for each gel isgiven here in Newtons (N) rather than N/m², since the various gelsamples all had the same cross-sectional area:

Ratio of laccase to Corn Bran Extract (LACU/g) Force (N) 0.18 0.20 1.800.44 18.0 0.71

EXAMPLE 2

Gelation of Sugar Beet Pectin

Solutions containing 1%, 2% and 3% by weight (w/w), respectively, ofpectic material were prepared by dissolving different amounts of sugarbeet pectin [cf. F. Guillon and J. -F. Thibault, Carbohydr. Polym. 12(1990) 353-374 (vide supra); α-arabinofuranosidase suitable for thispurpose is obtainable from Megazyme, Australia] in aqueous 0.05 MNaH₂PO₄ buffer solution, adjusting the pH of each solution to 5.5 byaddition of 0.5 M NaOH, and adjusting the final pectin concentration ofeach solution by addition of distilled water. The solutions were thenthermostatted in a water bath at 30° C.

To samples of each pectin solution were added different amounts oflaccase preparation [Trametes villosa laccase; produced by Novo NordiskA/S, Bagsvaerd, Denmark] containing 275 LACU/g of laccase preparation.The resulting solutions were then stirred mechanically until gelationoccurred. The gels were then thermostatted at 30° C. overnight.

Each gel sample was washed by allowing it to stand in 300 ml ofdistilled water for 1-2 hours. Water was removed by filtration on asteel mesh filter. The individual gels were rinsed thoroughly withcopious amounts of water, washed with acetone (300 ml) and dried in avacuum drying oven at 30° C. overnight. The thus-dried products were cutinto pieces and comminuted in a small laboratory mill (Retsch UltraCentrifugal Mill ZM 1000, with ring sieve 6.0)

The following table shows the various combinations of pectinconcentration and laccase concentration employed in the preparation ofeach gel:

Pectin concn. Laccase concn. Gel No. (% w/w) (LACU/g pectin) 1 1 1.0 2 17.5 3 2 0.5 4 2 1.0 5 2 7.5 6 2 15 7 2 30 8 3 1.0 9 3 7.5 10  3 15 11  330

The Free Swelling Capacity (FSC; i.e. the liquid uptake per gram ofdried gel) and the Retention Capacity (RC; i.e. the liquid retention pergram of dried gel) of each of the dried gels was determined as follows:

FSC:

A 0.2 g sample of comminuted dried gel was placed in a fine-mesh nylon“teabag” (3.5×6 cm). The closed “teabag” was then immersed for 1 hour inan aqueous solution simulating human urine, and having the followingcomposition:

60 mM KCl, 130 mM NaCl, 3.5 mM MgCl₂.6H₂O, 2.0 mM CaCl₂.2H₂O, 300 mMurea, surface tension adjusted to 60 dynes/cm by addition of Triton™X-100 (Rohm & Haas) [surface tension measurements made with a CAHNDynamic Contact Angle Analyzer (Cahn Instrument Inc.) using the Wilhelmyplate technique].

The soaked “teabag” with contents was allowed to drip-dry for 2 minutes.The FSC for the gel in question was calculated by dividing the weight(in grams) of liquid absorbed by the gel sample in the teabag by theinitial weight (0.2 g) of the dry gel sample.

RC:

The drip-dried “teabag” was centrifuged (WIFUG laboratory centrifuge 500E) at 327×g for 10 minutes. RC for the gel in question was calculated bydividing the weight (in grams) of absorbed liquid remaining in theteabag after centrifugation by initial weight (0.2 g) of the dry gelsample.

The results of the FSC and RC measurements for the various gels areshown in the table below. The corresponding data for a sample ofungelled sugar beet pectin are included for comparison:

Dried Gel No. FSC (g/g) RC (g/g) 1 12  6 2 17 10 3 19 11 4 21 13 5 20 126 19 11 7 19 11 8 20 10 9 20 11 10  19 11 11  18 10 Ungelled pectin  3** **: the sample passed through the nylon mesh of the “teabag”

It is apparent from the above that dried gels prepared from phenolicpolysaccharides, in this case sugar beet pectin, in the manner accordingto the invention can exhibit excellent liquid-absorption andliquid-retention properties.

What is claimed is:
 1. A method for causing gelling or increase ofviscosity of an aqueous medium containing a gellable polymeric materialhaving substituents with phenolic hydroxy groups, the method comprisingadding to said aqueous medium an amount of a laccase effective forincreasing said viscosity.
 2. The method of claim 1, wherein saidgellable polymeric material is a polysaccharide having substituents withphenolic hydroxy groups.
 3. The method of claim 1, wherein the phenolicsubstituents are cinnamic acid ester groups.
 4. The method of claim 2,wherein the polysaccharide is an arabinoxylan or a material comprisingpectin.
 5. The method of claim 4, wherein the arabinoxylan is obtainablefrom a cereal.
 6. The method of claim 5, wherein the cereal is wheat ormaize.
 7. The method of claim 4, wherein the arabinoxylan is extractedfrom flour or bran.
 8. The method of claim 4, wherein the pecticmaterial is from a member of the family Chenopodiaceae.
 9. The method ofclaim 8, wherein the pectic material is from sugar beets.
 10. The methodof claim 9, wherein the pectic material is extracted from sugar beetpulp.
 11. The method of claim 1, wherein the gellable polymeric materialcones two or more polysaccharides having phenolic substituents.
 12. Themethod of claim 11, wherein the phenolic substituents are cinnamic acidester groups.
 13. The method of claim 11, wherein the gellable polymericmaterial comprises an arabinoxylan and a material comprising pectin. 14.The method of claim 13, wherein the arabinoxylan is a cerealarabinoxylan and the pectic material is beet pectin.
 15. The method ofclaim 14, wherein the cereal arabinoxylan is wheat or maize.
 16. Themethod of claim 1, wherein the laccase is derived from a microorganism.17. The method of claim 16, wherein the microorganism is a fungus. 18.The method of claim 17, wherein the laccase is derived from a member ofthe genus Trametes or the genus Myceliophthora.
 19. The method of claim18, wherein the laccase is derived from Trametes villosa or fromMyceliophthora thermophila.
 20. The method of claim 1, wherein theamount of laccase employed is in the range from 0.01 to 100 kLACU per kgof gellable polymeric material.
 21. The method of claim 13, wherein thegelled product is subjected to a drying or dehydration procedure.